Biodegradable aliphatic-aromatic copolyester

ABSTRACT

Biodegradable aliphatic/aromatic copolyester comprising 49 to 66 mol % of an aromatic polyfunctional acid; 51 to 34 mol % of an aliphatic acid, at least 70% of which is sebacic acid; and butandiol; and blends containing such copolyester.

RELATED APPLICATIONS

This application is a national stage (under 35 U.S.C. §371) ofPCT/EP2006/002672 filed Mar. 17, 2006, which claims benefit of Italianapplication MI2005A000452 filed Mar. 18, 2005, disclosure of which areincorporated herein by reference.

The present invention relates to a biodegradable aliphatic-aromaticpolyester (AAPE) obtained from an aliphatic acid at least 70% of whichis sebacic acid, at least a polyfunctional aromatic acids and at least adialcohol, as well as to mixtures of said polyesters with otherbiodegradable polymers both of natural origin and of synthetic origin.

Biodegradable aliphatic-aromatic polyesters obtained from dicarboxylicacids and dialcohols are known in the literature and are commerciallyavailable. The presence of the aromatic component in the polyester chainis important to obtain polymers with sufficiently high melting pointsand with adequate crystallization rates.

Although polyesters of this sort are currently commercially available,the amount of aromatic acid in the chain is typically lower than 49%since the above said threshold, the percentage of biodegradation of thepolyesters decreases significantly above said threshold.

It is reported in the literature (Muller et al., Angew. Chem., Int., Ed.(1999), 38, pp. 1438-1441) that copolymers of the polybutyleneadipate-co-terephthalate type with a molar fraction of terephthalate of42 mol %, biodegrade completely to form compost in twelve weeks, whereasproducts with 51 mol % of molar fraction of terephthalate show apercentage of biodegradation of less than 40%. This different behaviourwas attributed to the formation of a higher number of butyleneterephthalate sequences with a length greater than or equal to 3, whichare less easily biodegradable. If it were possible to maintain suitablebiodegradation properties, an increase in the percentage of aromaticacid in the chain would, however, be desirable in so far as it wouldenable an increase in the melting point of the polyester, an increasein, or at least a maintenance of, important mechanical properties, suchas ultimate strength and elastic modulus, and would moreover enable anincrease in the crystallization rate of the polyester, thereby improvingits industrial processability.

A further drawback of biodegradable aliphatic-aromatic polyesters thatare currently commercially available is represented by the fact that themonomers of which they are constituted come from non-renewable sources,thereby maintaining a significant environmental impact associated to theproduction of such polyesters despite their biodegradability. They havefar more energy content than LDPE and HDPE particularly in the presenceof adipic acid. On the other hand, the use of monomers of vegetal originwould contribute to the reduction of emission of CO₂ in the atmosphereand to the reduction in the use of monomers derived from non-renewableresources.

U.S. Pat. No. 4,966,959 discloses certain copolyesters comprising from60 to 75% mol of terephtalic acid, 25 to 40% mol of a carboxylicaliphatic or cycloaliphatic acid, and a glycol component. The inherentviscosity of such polyesters is from about 0.4 to about 0.6, renderingthe polyesters useful as adhesives but unsuitable for many otherapplications.

U.S. Pat. No. 4,398,022 discloses copolyesters comprising terephtalicacid and 1,12-dodecanedioic acid and a glycol component comprising1,4-cyclohexanedimethanol. The acid component may optionally include oneor more acids conventionally used in the production of polyesters, butthe examples show that 1,12-dodecanedioic acid must be present for thepolyesters to have the desired melt strength.

U.S. Pat. No. 5,559,171 discloses binary blends of cellulose esters andaliphatic-aromatic copolyesters. The AAPE component of such blendscomprises a moiety derived from a C₂-C₁₄ aliphatic diacid which canrange from 30 to 95% mol in the copolymer, a moiety derived from anaromatic acid which can range from 70 to 5% mol in the copolymer.Certain AAPEs disclosed in this document do not require blending and areuseful in film application. They comprise a moiety derived from a C₂-C₁₀aliphatic diacid which can range from 95 to 35% mol in the copolymer,and a moiety derived from an aromatic acid which can range from 5 to 65%mol in the copolymer.

DE-A-195 08 737 discloses biodegradable AAPEs comprising terephtalicacid, an aliphatic diacid and a diol component. The weight averagemolecular weight M_(w) of such AAPEs is always very low (maximum 51000g/mol), so that their industrial applicability is limited.

It is therefore the overall object of the present invention to disclosean improved AAPE and blends containing the same.

In fact, the present invention regards a biodegradablealiphatic/aromatic copolyester (AAPE) comprising:

A) an acid component comprising repeating units of:

-   -   1) 49 to 66 mol %, preferably 49.5 to 63, more preferably 50 to        61%, of an aromatic polyfunctional acid;    -   2) 51 to 34%, preferably 50.5 to 37%, and more preferably 50 to        39 mol %, of an aliphatic acid, at least 70% of which,        preferably 90% of which, is sebacic acid;

B) butandiol;

said AAPE being biodegradable according to the Standard ISO 14855Amendment 1 of more than 40%, preferably more than 60%, in 30 days, withrespect to cellulose used as reference, and having:

-   -   a density of less than 1.22 g/cc, preferably less than 1.21        g/cc, and more preferably less than 1.20 g/cc;    -   a number average molecular weight M_(n) of 40,000-140,000    -   an inherent viscosity of 0.8-1.5.

By “polyfunctional aromatic acids” for the purposes of the presentinvention are meant aromatic dicarboxylic compounds of the phthalic-acidtype and their esters, preferably terephthalic acid.

The content of aromatic dicarboxylic acid in the biodegradable polyesteraccording to the claims of the present invention is 49 to 66 mol % andpreferably 49.5-63, more preferably 50-61% with respect to the totalmolar content of the acid component.

The molecular weight M_(n) of the polyester according to the presentinvention is between 40 000 and 140 000. The polydispersity indexM_(w)/M_(n) determined by means of gel-permeation chromatography (GPC)is between 1.7 and 2.6, preferably between 1.8 and 2.5.

The polyester according to the invention is characterized from beingrapidly crystallizable and has a crystallization temperature T_(c)higher than 30° C., preferably higher than 40° C.

The polyester according to the invention has an inherent viscosity(measured with Ubbelhode viscosimeter for solutions in CHCl₃ of aconcentration of 0.2 g/dl at 25° C.) of between 0.8 dl/g and 1.5 dl/g,preferably between 0.83 dl/g and 1.3 dl/g and even more preferablybetween 0.85 dl/g and 1.2 dl/g.

The Melt Flow Rate (MFR) of the polyester according to the invention, inthe case of use for applications typical of plastic materials (such as,for example, bubble filming, injection moulding, foams, etc.), isbetween 0.5 and 100 g/10 min, preferably between 1.5-70 g/10 min, morepreferably between 2.0 and 50 g/10 min (measurement made at 190° C./2.16kg according to the ASTM D1238 standard).

The polyester has a density measured with a Mohr-Westphal weighingmachine of less than 1.22 g/cm2, preferably less than 1.21 g/cm2 andeven more preferably less than 1.20 g/cm2.

Advantageously the polyester according to the present invention shows aenergy at break higher than 80 MJ/m2 preferably higher than 100 MJ/m²and -a Elastic Modulus higher than 75 MPa.

Advantageously, the polyester according to the present invention show anElmendorf tear strength (determined according to the standard ASTMD1922-89 and measured on blown film filmed with a blowing ratio of 2-3and a draw down ratio of 7-14) higher than 20 N/mm, preferably higherthan 25 N/mm, in the longitudinal direction and higher than 60 N/mm,preferably higher than 65 N/mm, for the quantity:(cross direction+longitudinal direction)/2

The aliphatic acid A2 which can be different from sebacic acid cancomprise or consist of at least one hydroxy acid or one dicarboxylicacid different from sebacic acid, such as azelaic and brassylic acid, inan amount of up to 30% mol, preferably 10 mol %, with respect to thetotal molar content of sebacic acid.

Examples of suitable hydroxy acids are glycolic acid, hydroxybutyricacid, hydroxycaproic acid, hydroxyvaleric acid, 7-hydroxyheptanoic acid,8-hydroxycaproic acid, 9-hydroxynonanoic acid, lactic acid or lactide.The hydroxy acids can be inserted in the chain as such, or else can alsobe previously made to react with diacids or dialcohols. The hydroxy acidunits can be inserted randomly in the chain or can form blocks ofadjacent units.

In the process of preparation of the copolyester according to theinvention one or more polyfunctional molecules, in amounts of between0.02-3.0 mol % preferably between 0.1 mol % and 2.5 with respect to theamount of dicarboxylic acids (as well as to the possible hydroxy acids),can advantageously be added in order to obtain branched products.Examples of these molecules are glycerol, pentaerythritol, trimethylolpropane, citric acid, dipentaerythritol, monoanhydrosorbitol,monohydromannitol, epoxidized oils such as epoxidized soybean oil,epoxidized linseed oil and so on, dihydroxystearic acid, itaconic acidand so on.

Although the polymer according to the present invention reach highlevels of performance without any need to add chain extenders such as diand/or poly isocyanates and isocyanurates, di and/or poly epoxides,bis-oxazolines or poly carbodimides or divinylethers, it is in any casepossible to modify the properties thereof as the case may require.

Generally such additives are used in percentages comprised between0.05-2.5%, preferably 0.1-2.0%. In order to improve the reactivity ofsuch additives, specific catalysts can be used such as for example zincstearates (metal salts of fatty acids) for poly epoxides.

The increase in the molecular weight of the polyester can advantageouslybe obtained, for example, by addition of various organic peroxidesduring the process of extrusion. The increase in molecular weight of thebiodegradable polyester can be easily detected by observing the increasein the values of viscosity following upon treatment of the polyesterswith peroxides.

In case of use of the polyesters according to the present invention forthe production of films, the addition of the above mentioned chainextenders according to the teaching of EP 1 497 370 results in aproduction of a gel fraction lower than 4.5% w/w with respect to thepolyester. In this connection the content of EP 1 497 370 has to beintended as incorporated by reference in the present description.

The polyester according to the invention present properties and valuesof viscosity that render them suitable for use, by appropriatelymodulating the relative molecular weight, in numerous practicalapplications, such as films, injection-moulded products,extrusion-coating products, fibres, foams, thermoformed products,extruded profiles and sheets, extrusion blow molding, injection blowmolding, rotomolding, stretch blow molding etc.

In case of films, production technologies like film blowing, casting,coextrusion can be used. Moreover such films can be subject tobiorientation in line or after film production. The films can be alsooriented through stretching in one direction with a stretching ratiofrom 1:2 up to 1:15, more preferably from 1:2.2 up to 1:8. It is alsopossible that the stretching is obtained in presence of an highly filledmaterial with inorganic fillers. In such a case, the stretching cangenerate microholes and the so obtained film can be particularlysuitable for hygiene applications.

In particular, the polyester according to the invention is suitable forthe production of:

-   -   films, whether one-directional or two-directional, and        multilayer films with other polymeric materials;    -   films for use in the agricultural sector as mulching films;    -   cling films (extensible films) for foodstuffs, for bales in the        agricultural sector and for wrapping of refuse;    -   shrink film such as for example for pallets, mineral water, six        pack rings, and so on;    -   bags and liners for collection of organic matter, such as        collection of refuse from foodstuffs, and for gathering mowed        grass and yard waste;    -   thermoformed single-layer and multilayer packaging for        foodstuffs, such as for example containers for milk, yoghurt,        meat, beverages, etc.;    -   coatings obtained with the extrusion-coating technique;    -   multilayer laminates with layers of paper, plastic materials,        aluminium, metallized films;    -   foamed or foamable beads for the production of pieces formed by        sintering;    -   foamed and semi-foamed products including foamed blocks made up        of pre-foamed particles;    -   foamed sheets, thermoformed foamed sheets, containers obtained        therefrom for the packaging of foodstuffs;    -   containers in general for fruit and vegetables;    -   composites with gelatinized, destructured and/or complexed        starch, natural starch, flours, other fillers of natural,        vegetal or inorganic origin;    -   fibres, microfibres, composite fibres with a core constituted by        rigid polymers, such as PLA, PET, PTT, etc. and an external        shell made with the material according to the invention, dablens        composite fibres, fibres with various sections (from round to        multilobed), flaked fibres, fabrics and non-woven fabrics or        spun-bonded or thermobonded fabrics for the sanitary sector, the        hygiene sector, the agricultural sector, georemediation,        landscaping and the clothing sector.

The polyester according to the invention can moreover be used in blends,obtained also by reactive extrusion, whether with polyesters of the sametype (such as aliphatic/aromatic copolyester as for example polybutylentereptalate adipate PBTA, polybutylen tereftalatesuccinate PBTS andpolybutylen tereftalateglutarate PBTG) or with other biodegradablepolyesters (for example, polylactic acid, poly-ε-caprolactone,polyhydroxybutyrates, such as poly-3-hydroxybutyrates,poly-4-hydroxybutyrates and polyhydroxybutyrate-valerate,polyhydroxybutyrate-propanoate, polyhydroxybutyrate-hexanoate,polyhydroxybutyrate-decanoate, polyhydroxybutyrate-dodecanoate,polyhydroxybutyrate-hexadecanoate, polyhydroxybutyrate-octadecanoate,and polyalkylene succinates and their copolymers with adipic acid,lactic acid or lactide and caprolacton and their combinations)), orother polymers different from polyesters. Mixtures of the polyester withpolylactic acid are particularly preferred.

The polyester according to the invention can also be used in blends withpolymers of natural origin, such as for example starch, cellulose,chitosan, alginates, natural rubbers or natural fibers (such as forexample jute, kenaf, hemp) The starches and celluloses can be modified,and amongst these starch or cellulose esters with a degree ofsubstitution of between 0.2 and 2.5, hydroxypropylated starches, andmodified starches with fatty chains may, for example, be mentioned.Preferred esters are acetates, propionates, butyrrates and theircombinations. Starch can moreover be used both in its destructurizedform and in its gelatinized form or as filler. Mixtures of the AAPEaccording to the invention with starch are particularly preferred.

Mixtures of the AAPE according to the present invention with starch canform biodegradable polymeric compositions with good resistance to ageingand to humidity. In these compositions, which comprise thermoplasticstarch and a thermoplastic polymer incompatible with starch, starchconstitutes the dispersed phase and the AAPE thermoplastic polymerconstitutes the continuous phase.

The polymeric compositions can maintain a high tear strength even inconditions of low humidity. Such characteristic is obtained when starchis in the form of a dispersed phase with an average dimension lower than1 μm. The preferred average numeral size of the starch particles isbetween 0.1 and 0.5 microns and more than 80% of the particles have asize of less than 1 micron.

Such characteristics can be achieved when the water content of thecomposition during mixing of the components is preferably kept between 1and 15%. It is, however, also possible to operate with a content of lessthan 1% by weight, in this case, starting with predried andpre-plasticized starch.

It could be useful also to degrade starch at a low molecular weightbefore or during compounding with the polyesters of the presentinvention in order to have in the final material or finished product astarch inherent viscosity between 1 and 0.2 dl/g, preferably between 0.6and 0.25 dl/g, more preferably between 0.55 and 0.3 dl/g. Destructurizedstarch can be obtained before of during mixing with the AAPE of thepresent invention in presence of plasticizers such as water, glycerol,di and polyglycerols, ethylene or propylene glycol, ethylene andpropylene diglycol, polyethylene glycol, polypropylenglycol, 1,2propandiol, trymethylol ethane, trimethylol propane, pentaerytritol,dipentaerytritol, sorbitol, erytritol, xylitol, mannitol, sucrose, 1,3propandiol, 1,2, 1,3, 1,4 buthandiol, 1,5 pentandiol, 1,6, 1,5hexandiol, 1,2,6, 1,3,5-hexantriol, neopenthil glycol, and polyvinylalcohol prepolymers and polymers, polyols acetates, ethoxylates andpropoxylates, particularly sorbitol ethoxylate, sorbitol acetate, andpentaerytritol acetate. The quantity of high boiling point plasticizers(plasticizers different from water) used are generally from 0 to 50%,preferably from 10 to 30% by weight, relative to starch.

Water can be used as a plasticizer in combination with high boilingpoint plasticizers or alone during the plastification phase of starchbefore or during the mixing of the composition and can be removed at theneeded level by degassing in one or more steps during extrusion. Uponcompletion of the plastification and mixing of the components, the wateris removed by degassing to give a final content of about 0.2-3% byweight.

Water as well as high-boiling point plasticizers modify the viscosity ofthe starch phase and affect the Theological properties of thestarch/polymer system, helping to determine the dimensions of thedispersed particles. Compatibilizers can be also added to the mixture.They can belong to the following classes:

-   -   Additives such as esters which have hydrophilic/lipophilic        balance index values (HLB) greater than 8 and which are obtained        from polyols and from mono or polycarboxylic acids with        dissociation constants pK lower than 4.5 (the value relates to        pK of the first carboxyl group in the case of polycarboxylic        acids.)    -   Esters with HLB values of between 5.5 and 8, obtained from        polyols and from mono or polycarboxylic acids with less than 12        carbon atoms and with pK values greater than 4.5 (this value        relates to the pK of the first carboxylic group in the case of        polycarboxylic acids).    -   Esters with HLB values lower than 5.5 obtained from polyols and        from fatty acids with 12-22 carbon atoms.

These compatibilizers can be used in quantities of from 0.2 to 40%weight and preferably from 1 to 20% by weight related to the starch. Thestarch blends can also contain polymeric compatibilizing agents havingtwo components: one compatible or soluble with starch and a second onesoluble or compatible with the polyester.

Examples are starch/polyester copolymers through transesterificationcatalysts. Such polymers can be generated trough reactive blendingduring compounding or can be produced in a separate process and thenadded during extrusion. In general block copolymers of an hydrophilicand an hydrophobic units are particularly suitable.

Additives such as di and polyepoxides, di and poly isocyanates,isocyanurates, polycarbodiimmides and peroxides can also be added. Theycan work as stabilizers as well as chain extenders.

All the products above can help to create the needed microstructure. Itis also possible to promote in situ reactions to create bonds betweenstarch and the polymeric matrix. Also aliphatic-aromatic polymers chainextended with aliphatic or aromatic diisocyanates or di and polyepoxidesor isocyanurates or with oxazolines with intrinsic viscosities higherthan 1 dl/g or in any case aliphatic-aromatic polyesters with a ratiobetween Mn and MFI at 190° C., 2.16 kg higher than 10 000, preferablyhigher than 12 500 and more preferably higher than 15 000 can also beused to achieve the needed microstructure.

Another method to improve the microstructure is to achieve starchcomplexation in the starch-polyester mixture.

In such a case, in the X-Ray spectra of the compositions with thepolyester according to the present invention, the Hc/Ha ratio betweenthe height of the peak (Hc) in the range of 13-14° of the complex andthe height of the peak (Ha) of the amorphous starch which appears atabout 20.5° (the profile of the peak in the amorphous phase having beenreconstructed) is less than 2 and greater than 0.02.

The starch polyester ratio is comprised in the range 5/95% weight up to60/40% by weight, more preferably 10/90-45/55% by weight. In suchstarch-based blends in combination with the polyesters of the presentinvention it is possible to add polyolefins, polyvynil alcohol at highand low hydrolysis degree, ethylene vinylalcohol and ethylenevinylacetate copolymers and their combinations as well as aliphaticpolyesters such as polybuthylensuccinate, polybuthylensuccinate adipate,polybuthylensuccinate adipate-caprolactate,polybuthylensuccinate-lactate, polycaprolactone polymers and copolymers,PBT, PET, PTT, polyamides, polybuthylen terephtalate adipates with acontent of terephtalic acid between 40 and 70% with and withoutsolfonated groups with or without branchs and possibly chain extendedwith diisocyanates or isocyanurates, polyurethanes, polyamide-urethanes,cellulose and starch esters such as acetate, propionate and butyratewith substitution degrees between 1 and 3 and preferably between 1.5 and2.5, polyhydroxyalkanoates, poly Llactic acid, polyD lactic acid andlactides, their mixtures and copolymers.

The starch blends of the polyesters of the present invention maintain abetter ability to crystallize in comparison with compostable starchblends where copolyester are poly buthylen adipate terephtalates atterephtalic content between 45 and 49% (range of the product withindustrial performances) and can be easily processable in film blowingeven at MFI (170° C., 5 kg) of 7 g/10 min due to the highcrystallization rate of the matrix. Moreover they have impact strengthhigher than 20 kj/m2, preferably higher than 30 kj/m2 and mostpreferably higher than 45 kj/m2 (measured on blown film 30 um thick at10° C. and less then 5% relative humidity).

Particularly resistant and easily processable compounds containdestructurized starch in combination with the polyesters of theinvention and polylactic acid polymers and copolymers with and withoutadditives such as polyepoxydes, carbodiimmides and/or peroxides.

The starch-base films can be even transparent in case of nanoparticlesof starch with dimensions lower than 500 μm and preferably lower than300 μm.

It is also possible to go from a dispersion of starch in form ofdroplets to a dispersion in which two co-continuous phases coexist andthe blend is characterized for allowing a higher water content duringprocessing.

In general, to obtain co-continuous structures it is possible to workeither on the selection of starch with high amylopectine content and/orto add to the starch-polyester compositions block copolymers withhydrophobic and hydrophilic units. Possible examples arepolyvynilacetate/polyvinylalcohol and polyester/polyether copolymers inwhich the block length, the balance between the hydrophilicity andhydrophobicity of the blocks and the quality of compatibilizer used canbe suitably changed in order to finely adjust the microstructure of thestarch-polyester compositions.

The polyester according to the invention can also be used in blends withthe polymers of synthetic origin and polymers of natural originmentioned above. Mixtures of polyesters with starch and polylactic acidare particularly preferred.

Blends of the AAPE according the present invention with PLA are ofparticular interest because the high crystallization rate of thealiphatic-aromatic polyester of the invention and its high compatibilitywith PLA polymers and copolymers permits to cover materials with a widerange of rigidities and high speed of crystallization which makes theseblends particularly suitable for injection molding and extrusion.

Moreover, blends of such polyester with poly L lactic acid and poly Dlactic acid or poly L lactide and D lactide where the ratio between polyL and poly D lactic acid or lactide is in the range 10/90-90/10 andpreferably 20/80-80/20 and the ratio between aliphatic-aromaticpolyester and the polylactic acid or PLA blend is in the range 5-95-95/5and preferably 10/90-90/10 are of particular interest for the highcrystallization speed and the high thermal resistance. Polylactic acidor lactide polymers or copolymers are generally of molecular weight Mnin the range between 30 000 and 300 000 and more preferably between 50000 and 250 000.

To improve the transparency and thoughness of such blends and decreaseor avoid a lamellar structure of polylactide polymers it could bepossible to introduce other polymers as compatibilizers or tougheningagents such as polybuthylen succinate and copolymers with adipic acidand or lactic acid and or hydroxyl caproic acid, or polycaprolactone oraliphatic polymers of diols from C2 to C13 and diacids from C4 to C13 orpolyhydroxyalkanoates or polyvynilalcohol in the range of hydrolysisdegree between 75 and 99% and its copolymers or polyvynilacetate in arange of hydrolysis degree between 0 and 70%, preferably between 0 and60%. Particularly preferred as diols are ethylene glycol, propandiol,butandiol and as acids: azelaic, sebacic, undecandioic acid,dodecandioic acid and brassilic acid and their combinations.

To maximize compatibility among the AAPE of the invention and polylactic acid it is very useful the introduction of copolymers with blockshaving high affinity for the aliphatic-aromatic copolyester of theinvention and blocks with affinity for the poly lactic acid polymers orcopolymers. Particularly preferred examples are block copolymers of thealiphatic aromatic copolymer of the invention with polylactic acid. Suchblock copolymers can be obtained taking the two original polymersterminated with hydroxyl groups and then reacting such polymers withchain extenders able to react with hydroxyl groups such asdiisocyanates. Examples are 1,6 esamethylendiisocianate,isophorondiisocyanate, methylendiphenildiisocyanate, toluendiisocianateor the like. It is also possible to use chain extenders able to reactwith acid groups like di and poly epoxides (e.g. bisphenols diglycidylethers, glycerol diglycidyl ethers), divinyl derivatives if the polymersof the blend are terminated with acid groups.

It is possible also to use as chain extenders carbodiimmides,bis-oxazolines, isocianurates etc.

The intrinsic viscosity of such block copolymers can be between 0.3 and1.5 dl/g, more preferred are between 0.45 and 1.2 dl/g. The amount ofcompatibilizer in the blend of aliphatic aromatic copolyesters andpolylactic acid can be in the range between 0.5 and 50%, more preferablybetween 1 and 30%, more preferably between 2 and 20% by weight.

The AAPE according to the present invention can advantageously beblended also with filler both of organic and inorganic naturepreferably. The preferred amount of fillers is in the range of 0.5-70%by weight, preferably 5-50% by weight.

As regards organic fillers wood powder, proteins, cellulose powder,grape residue, bran, maize husks, compost, other natural fibres, cerealgrits with and without plasticizers such as polyols can be mentioned.

As regards inorganic fillers, it can be mentioned substances able to bedispersed and/or to be reduced in lamellas with submicronic dimensions,preferably less than 500 nm, more preferably less than 300 nm, and evenmore preferably less than 50 nm. Particularly preferred are zeolites andsilicates of various kind such as wollastonites, montmorillonites,hydrotalcites also functionalised with molecules able to interact withstarch and or the specific polyester. The use of such fillers canimprove stiffness, water and gas permeability, dimensional stability andmaintain transparency.

The process of production of the polyester according to the presentinvention can be carried out according to any of the processes known tothe state of the art. In particular the polyesters can be advantageouslyobtained with a polycondensation reaction.

Advantageously, the process of polymerization of the copolyester can beconducted in the presence of a suitable catalyst. As suitable catalysts,there may be cited, by way of example, metallo-organic compounds of tin,for example derivatives of stannoic acid, titanium compounds, forexample orthobutyl titanate, and aluminium compounds, for exampletriisopropyl aluminium, antimony compounds, and zinc compounds.

EXAMPLES

In the examples provided hereinafter,

-   -   MFR was measured in the conditions envisaged by the ASTM        D1238-89 standard at 150° C. and 5 kg or at 190° C. and 2.16 kg;    -   the melting and crystallization temperatures and enthalpies were        measured with a differential scanning calorimeter Perkin Elmer        DSC7, operating with the following thermo profile:        -   1st scan from −30° C. to 200° C. at 20° C./min        -   2nd scan from 200° C. to −30° C. at 10° C./min        -   3rd scan from −30° C. to 200° C. at 20° C./min    -   T_(m1) was measured as endothermic-peak value of the 1st scan,        and T_(m2) as that of the 3rd scan; T_(c) was measured as        exothermic-peak value of the 2nd scan.    -   Density

Determination of Density according to the Mohr Westphal method has beenperformed with an analytical balance Sartorius AC 120S equipped with aSartorius Kit YDK 01. The Kit is provided with two small baskets. Oncethe Kit has been mounted, ethanol has been introduced in thecrystallizer. The balance has been maintained at room temperature.

Each test has been performed with about 2 g of polymer (one or morepellets).

The density d has been determined according to the above formula:D=(W _(a) /G)d _(fl)

W_(a): weight of the sample in air

W_(fl): weight of the sample in alcoholG=W _(a) −W _(fl)

d_(fl)=ethanol density at room temperature (Values read on tablesprovided by the company Sartorius with the Kit).

The experimental error of the Density values is in the range of±2.5×10⁻³.

-   -   η_(in) has been determined according to the ASTM 2857-87        standard.    -   M_(n) has been determined on a Agilent 1100 Series GPC system        with chloroform as eluent and polystyrene standards for the        calibration curve.

Example 1

A 25-l steel reactor, provided with a mechanical stirrer, an inlet forthe nitrogen flow, a condenser, and a connection to a vacuum pump wascharged with:

2890 g of terephthalic acid (17.4 mol),

3000 g of sebacic acid (14.8 mol),

3500 g butandiol (38.9 mol),

6.1 g of butylstannoic acid.

The molar percentage of terephthalic acid with respect to the sum of thedicarboxylic acids was 54.0 mol %.

The temperature of the reactor was then increased up to 200° C., and anitrogen flow was applied. After approximately 90% of the theoreticalamount of water had been distilled, the pressure was gradually reducedto a value of less than 3 mmHg, and the temperature was raised to 240°C.

After approximately 3 hours, the molten product was poured from thereactor, cooled in a water bath and granulated. During the latteroperations it was possible to note how the product starts to solidifyrapidly and can be easily granulated. The product obtained had aninherent viscosity (measured in chloroform at 25° C., c=0.2 g/dl)η_(in)=0.93 (dl/g), Mn=52103, MFR (190° C.; 2.16 kg)=20 g/10 min and adensity of 1.18 g/cm2.

From H-NMR analysis a percentage of aromatic units was found of53.5±0.5%.

Example 2

The reactor as per Example 1 was charged with the same ingredient ofExample 1:

2890 g of terephthalic acid (17.4 mol),

3000 g of sebacic acid (14.8 mol),

3500 g butandiol (38.9 mol),

6.1 g of butylstannoic acid.

The molar percentage of terephthalic acid with respect to the sum of thedicarboxylic acids being 54.0 mol %.

The reaction has been carried out for the time necessary to obtain aproduct having an inherent viscosity (measured in chloroform at 25° C.,c=0.2 g/dl) η_(in)=1.03 (dl/g), M_(n)=58097, MFR (190° C.; 2.16 kg)=14.8g/10 min and a density of 1.18 g/cm2.

Example 3

The process of Example 1 was repeated with:

-   -   3476.48 g of dimethyl tereftalate (17.92 mol)    -   3493.80 g of butandiol (38.82 mol)    -   2411.88 g of sebacic acid (11.94 mol)

The molar percentage of aromatic content with respect to the sum of theacids was 60 mol %.

A product was obtained with M_(n)=56613, M_(w)/M_(n)=2.0364 inherentviscosity (measured in chloroform at 25° C., c=0.2 g/dl) η_(in)=0.97(dl/g), density 120 g/cc and MFR (190° C.; 2.16 kg)=7.8 g/10 min.

Example 4 Comparison

The process of Example 1 was repeated with:

2480 g of terephthalic acid (14.9 mol),

3400 g of sebacic acid (16.8 mol),

3430 g butandiol (38.1 mol),

6.1 g of butylstannoic acid.

The molar percentage of terephthalic acid with respect to the sum of thecarboxylic acids was 47 mol %.

A product was obtained with inherent viscosity (measured in chloroformat 25° C., c=0.2 g/dl) η_(in)=1.00 (dl/g) and MFR (190° C.; 2.16 kg)=15g/10 min.

From H-NMR analysis, a percentage of aromatic units of 47.0±0.5% wasfound.

Example 5 (Comparison)

The process of Example 1 was repeated with:

3294.1 g of dimethyl terephthalate (16.98 mol),

3108.4 g of propandiol (40.9 mol),

2922.9 g of sebacic acid (11.94 mol).

The molar percentage of aromatic content with respect to the sum of theacids was 54 mol %.

A product was obtained with inherent viscosity (measured in chloroformat 25° C., c=0.2 g/dl) η_(in)=0.96 (dl/g), density 1.20 g/cc and MFR(190° C.; 2.16 kg)=g/10 min.

Example 6 Comparison

The process of Example 1 was repeated with:

3080.7 g of dimethyl terephthalate (15.88 mol),

3277.2 g of esandiol (27.77 mol),

2211.9 g of sebacic acid (11.94 mol)

The molar percentage of aromatic content with respect to the sum of theacids was 60 mol %.

A product was obtained with inherent viscosity (measured in chloroformat 25° C., c=0.2 g/dl) η_(in)=0.87 (dl/g), density 1.15 g/cc and MFR(190° C.; 2.16 kg)=g/10 min.

Example 7

The process of Example 1 was repeated with:

3858.7 g of dimethyl terephthalate (19.89 mol),

3526.4 g of butandiol (39.18 mol),

2070.5 g of sebacic acid (10.25 mol).

The molar percentage of aromatic content with respect to the sum of theacids was 66 mol %.

A product was obtained with inherent viscosity (measured in chloroformat 25° C., c=0.2 g/dl) η_(in)=0.90 (dl/g), density 1.21 g/cc and MFR(190° C.; 2.16 kg)=g/10 min.

The specimens of the examples were then filmed with the blow-filmtechnique, on Formac Polyfilm 20, equipped with metering screw 20C13,L/D=25, RC=1.3; air gap 1 mm; 30-50 RPM; T=140-180° C. The blow up ratiowas 2.5 whereas the draw down ratio was 10. The films thus obtained hada thickness of approximately 30μ.

A week after filming, and after conditioning at 25° C., with 55%relative humidity, the tensile properties were measured according to theASTM D882-88 standards.

Appearing in Table 1 are the thermal properties of the materials of theexamples, whilst Table 2 gives the mechanical properties of the films.

TABLE 1 Thermal properties Example Aromatic T_(m1) ΔH_(m1) T_(c) ΔH_(c)T_(m2) 1 53.5%   133 28 58 20 130 2 54% — — 46 19 129 3 60% — — 78 25146 4 (comp.) 47% — — 22 19 114 5 (comp.) 54% — — 54 20 132 6 (comp.)60% — — 23 22 80 7 66 — — 98 26 162

TABLE 2 Mechanical properties EXAMPLE 4 5 6* 1 2 3 (comp (comp (comp) 7Tensile properties - longitudinal Yield point 11 8 12 6.5 7.5 5 11.5(MPa) Ultimate 40 39 45 28 15 6.5 39.5 strength (MPa) Elastic 90 80 13065 110 85 165 modulus (MPa) Energy 143 161 154 135 75 42 155 at break(MJ/m2) Elmendorf tear strength (N/mm) (A) Cross 100 >126 >140 >110 19 —160 direction (B) 27 37 28 16 11 — 170 Longitudinal direction (A + B)/263.5 >81.5 >84 >63 15 — 165 *The Elmendorf values of Example 6 could notbe detected due to the extremely poor quality of the film

Biodegradation Test

For the materials of Examples 1-7 the biodegradation test was conductedin controlled composting according to the Standard ISO 14855 Amendment1.

The tests were conducted on 30-micron films ground in liquid nitrogenuntil they were fragmented to sizes of less than 2 mm or on pelletsground to particles having diameter <250 μ.m. As positive controlmicrocrystalline cellulose Avicel® for column chromatography lot No.K29865731 202 was used. Powder grain size: 80% between 20 μm and 160 μm;20% less than 20 μm.

TABLE 3 BIODEGRADATION Example Aromatic % biodegradation 1 53.5%   91 254% 90 3 60% 90 4 (comp.) 47% 100 5 (comp.) 54% 30 6 (comp.) 60% 71 766% 50

TABLE 4 DENSITY Example Aromatic Diacid/ Density 1 53.5% Sebacic 1.18 254 Sebacic 1.18 3 60 Sebacic 1.20 4 (comp.) 47 Sebacic 1.17 5 54 Sebacic1.20 6 60 Sebacic 1.15 7 66 Sebacic 1.21

1. A biodegradable aliphatic/aromatic copolyester (AAPE) comprising: A)an acid component comprising repeating units of: 1) 49 to 66 mol % of anaromatic polyfunctional acid; 2) 51 to 34% of an aliphatic acid, atleast 70% of which, is sebacic acid; B) butanediol; said AAPE beingbiodegradable according to the Standard ISO 14855 Amendment 1 of morethan 40% in 30 days, with respect to cellulose used as reference, andhaving: a density of less than 1.22 g/cc; a number average molecularweight M_(n) of 40,000 to 140,000; an inherent viscosity of 0.8 to 1.5;a polydispersity index M_(w)/M_(n) of between 1.8 and 2.5.
 2. Abiodegradable aliphatic/aromatic copolyester according to claim 1,wherein said acid component comprises 49.5 to 63 mol % of an aromaticpolyfunctional acid (A1); and 50.5 to 37% of an aliphatic acid (A2), atleast 70% of which is sebacic acid.
 3. A biodegradablealiphatic/aromatic copolyester according to claim 1, wherein said acidcomponent comprises 50 to 61 mol % of an aromatic polyfunctional acid(A1); and 50 to 39% of an aliphatic acid (A2), at least 70% of which issebacic acid.
 4. A biodegradable aliphatic/aromatic copolyesteraccording to claim 1, wherein said aliphatic acid A2 comprises at least90% of sebacic acid.
 5. A biodegradable aliphatic/aromatic copolyesteraccording to claim 1, wherein said biodegradability is more than 60%. 6.A biodegradable aliphatic/aromatic copolyester according to claim 1,wherein said density is less than 1.21 g/cc.
 7. A biodegradablealiphatic/aromatic copolyester according to claim 1, wherein saiddensity is less than 1.20 g/cc.
 8. A biodegradable aliphatic/aromaticcopolyester according to claim 1, wherein the aliphatic acid A2comprises at least one hydroxyl acid or one dicarboxylic acid differentfrom sebacic acid, in an amount of up to 30% mol with respect to thetotal molar content of sebacic acid.
 9. A biodegradablealiphatic/aromatic copolyester according to claim 8, wherein thealiphatic acid A2 comprises at least one hydroxyl acid or onedicarboxylic acid different from sebacic acid, in an amount of up to 10%mol with respect to the total molar content of sebacic acid.
 10. Abiodegradable aliphatic/aromatic copolyester according to claim 1, inwhich the aromatic polycarboxylic acid is a compound of a phthalic-acid.11. A biodegradable aliphatic/aromatic copolyester according to claim 1,being rapidly crystallizable and by having a crystallization temperatureT_(c) higher than 30° C.
 12. A biodegradable aliphatic/aromaticcopolyester according to claim 11, being rapidly crystallizable and byhaving a crystallization temperature T_(c) higher than 40° C.
 13. Abiodegradable aliphatic/aromatic copolyester according to claim 1,having an energy at break higher than 80 MJ/M².
 14. A polyesteraccording to claim 13, having an energy at break higher than 100 MJ/m².15. A biodegradable aliphatic/aromatic copolyester according to claim 1,having a Elmendorf tear strength higher than 20 N/mm in the longitudinaldirection, and higher than 0 N/mm for the quantity:(cross direction+longtitudinal direction)/2.
 16. A biodegradablealiphatic/aromatic copolyester according to claim 15, having anElmendorf tear strength higher than 25 N/mm in the longitudinaldirection, and higher than 65 N/mm, for the quantity:(cross direction+longitudinal direction)/2.
 17. A biodegradablealiphatic/aromatic copolyester according to claim 1, used in blends,obtained also by means of reactive extrusion, both with polyesters ofthe same type and with other biodegradable polymers whether of naturalorigin or of synthetic origin.
 18. A film comprising the biodegradablealiphatic/aromatic copolyester according to claim 1.